Energy Barricade Technical Details
Notes:
Although ProActive Energy Systems Energy Barricade BLOCKS 97% of radiant heat, your utility bills savings will vary because there are other forms of heat flow in a building that contribute to the total cooling (or heating) load. Data varies by region.
Points from a study performed by the Tennessee Valley Authority help to point out the utility bill savings you can expect:
- All the configurations tested yielded sizable percent savings (17%, based on Energy Star Evaluation) and statistically significant reductions in summer attic heat transfer compared to the non-radiant barrier test case. Also, as the ambient temperature increased, the savings also increased.
- The barricade placed on top of the attic floor insulation was the best summer performer. It consistently showed heat flux reductions compared to the non-barricade test case of about 40% percent for almost all ambient temperatures and even showed savings (17% percent) during mild temperature and night summer conditions.
- All the configurations provided statistically significant reductions in winter attic heat fluxes in many, but not all, situations. The percent savings during night hours and during below 35 degree conditions, when heating loads were the highest, were usually sizable (from 6 to 23 percent) and the differences between energy barricade barrier configurations and the non-energy barricade test case were often statistically significant during these conditions.
Conductive: Direct contact. If you touch a pot on the stove, this is conductive heat transfer.
Convective: Steam, moisture. If you put your hand above a boiling pot, you will feel heat in the form of steam. This is convective heat transfer.
Radiant: Electromagnetic. Step outside on a sunny day and feel the sun’s rays on your face. You are feeling radiant heat transfer. All objects above absolute zero (-459.7 degrees F.) emit infrared rays in a straight line in all directions.
Conduction
CONDUCTION is direct heat flow through matter (molecular motion). It results from actual PHYSICAL CONTACT of one part of the same body with another part, or of one body with another. For instance, if one end of an iron rod is heated, the heat travels by conduction through the metal to the other end; it also travels to the surface and is conducted to the surrounding air, which is another, but less dense, body. An example of conduction through contact between two solids is a cooking pot on the solid surface of a hot stove. The greatest flow of heat possible between materials is where there is a direct conduction between solids. Heat is always conducted from warm to cold, never from cold to warm, and always moves via the shortest and easiest route.
In general, the more dense a substance, the better conductor it is. Solid rock, glass and aluminum-being very dense-are good conductors of heat. Reduce their density by mixing air into the mass, and their conductivity is reduced. Because air has low density, the percentage of heat transferred by conduction through air is comparatively small. Two thin sheets of aluminum foil with about one inch of air space in between weigh less than one ounce per square foot. The ratio is approximately 1 of mass to 100 of air, most important in reducing heat flow by conduction. The less dense the mass, the less will be the flow of heat by conduction.
Convection
CONVECTION is the transport of heat within a gas or liquid, caused by the actual flow of the material itself (mass motion). In building spaces, natural convection heat flow is largely upward, somewhat sideways, not downward. This is called "free convection."
For instance, a warm stove, person, floor, wall, etc., loses heat by conduction to the colder air in contact with it. This added heat activates (warms) the molecules of the air which expand, becoming less dense, and rise. Cooler, heavier air rushes in from the side and below to replace it. The popular expression "hot air rises" is exemplified by smoke rising from a chimney or a Fire. The motion is turbulently upward, with a component of sideways motion. Convection may also be mechanically induced, as by a fan. This is called "forced convection."
Radiation
RADIATION is the transmission of electromagnetic rays through space. Radiation, like radio waves, is invisible. Infrared rays occur between light and radar waves (between the 3 -15 micron portion of the spectrum). Henceforth, when we speak of radiation, we refer only to infrared rays. Each material that has a temperature above absolute zero (-459-7 F.) emits infrared radiation, including the sun, icebergs, stoves or radiators, humans, animals, furniture, ceilings, walls, floors, etc.
All objects radiate infrared rays from their surfaces in all directions, in a straight line, until they are reflected or absorbed by another object. Traveling at the speed of light, these rays are invisible, and they have NO TEMPERATURE, only ENERGY. Heating an object excites the surface molecules, causing them to give off infrared radiation. When these infrared rays strike the surface of another object, the rays are absorbed and only then is heat produced in the object. This heat spreads throughout the mass by conduction. The heated object then transmits infrared rays from exposed surfaces by radiation if these surfaces are exposed directly to an air space.
The amount of radiation emitted is a function of the EMISSIVITY factor of the source's surface. EMISSIVITY is the rate at which radiation (EMISSION) is given off. Absorption of radiation by an object is proportional to the absorptivity factor of its surface which is reciprocal of its emissivity.
Although two objects may be identical, if the surface of one were covered with a material of 90% emissivity, and the surface of the other with a material of 5% emissivity, the result would be a drastic difference in the rate of radiation flow from these two objects. This is demonstrated by comparison of four identical, equally heated iron radiators covered with different materials. Paint one with aluminum paint and another with ordinary enamel. Cover the third with asbestos and the fourth with aluminum foil. Although all have the same temperature, the one covered with aluminum foil would radiate the least (lowest [3%] emissivity). The radiators covered with ordinary paint or asbestos would radiate most because they have the highest emissivity (even higher than the original iron). Painting over the aluminum paint or foil with ordinary paint changes the surface to 90% emissivity.
Materials whose surfaces do not appreciably reflect infrared rays, i.e.: paper, asphalt, wood, glass and rock, have absorption and emissivity rates ranging from 80% to 93%. Most materials used in building construction -- brick, stone, wood, paper, and so on -- regardless of their color, absorb infrared radiation at about 90%. It is interesting to note that a mirror of glass is an excellent reflector of light but a very poor reflector of infrared radiation. Mirrors have about the same reflectivity for infrared as a heavy coating of black paint.
The surface of aluminum has the ability NOT TO ABSORB, but TO REFLECT 97% of the infrared rays which strike it. Since aluminum foil has such a low mass to air ratio, very little conduction can take place, particularly when only 3% of the rays are absorbed.
TRY THIS EXPERIMENT: Hold a sample of FOIL INSULATION close to your face, without touching. Soon you will feel the warmth of your own infrared rays bounding back from the SURFACE. The explanation: The emissivity of heat radiation of the surface of your face is 99%- The absorption of aluminum is only 3%. It sends back 97% of the rays. The absorption rate of your face is 99%. The net result is that you feel the warmth of your face reflected.
Reflectivity and Air Spaces
In order to retard heat flow by conduction, walls and roofs are build with internal air spaces. Conduction and convection through these air spaces combined represent only 20% to 35% of the heat which pass through them. In both winter and summer, 65% to 80% of the heat that passes from a warm wall to a colder wall or through a ventilated attic does so by radiation.
The value of air spaces as thermal insulation must include the character of the enclosing surfaces. The surfaces greatly affect the amount of energy transferred by radiation, depending on the material's absorptivity and emissivity, and are the only way of modifying the total heat transferred across a given space. The importance of radiation cannot be overlooked in problems involving ordinary room temperatures.
Radiant barrier insulation is a reflective insulation system that offers a permanent way to reduce energy costs. Radiant barrier insulation systems reflect radiant heat energy instead of trying to absorb it. A pure aluminum radiant barrier reflective insulation is unaffected by humidity and will continue to perform at a consistent level no matter how humid it may be. A radiant barrier insulation system is a layer of foil facing an airspace and is installed in the envelope of a building.
Most people are familiar with traditional insulating materials such as fiberglass, cellulose, Styrofoam, and rock wool. These products use their ability to absorb or resist (slow down) convective and conductive heat transfer to insulate (R-value). A third, seldom discussed but dominant form of heat transfer exists: radiant heat transfer. What are the differences among the three forms of heat transfer?
A radiant barrier reflects radiant heat energy instead of trying to absorb it. What does this mean in your home or business? During the winter, 50-75% of heat loss through the ceiling/roofing system and 65-80% of heat loss through walls is radiant. In the summer, up to 93% of heat gain is radiant. If you are depending on R-value (resistance) alone to insulate against heat gain and loss, remember that thin layers of fiberglass are virtually transparent to radiant energy and are affected by changes in humidity (moisture levels). A 1-1/2% change in the moisture content of fiberglass insulation will result in a 36% decrease in performance (referenced from HVAC Manual 10.6; McGraw-Hill). A pure aluminum radiant barrier is unaffected by humidity and will continue to perform at a consistent level no matter how humid it may be.
Testing and Approvals
- Building Officials and Code Administrators
- International Conference of Building Officials
- Southern Building Code Congress International
- Metropolitan Dade County (FL) Building Code Compliance Dept.
- United States Testing Company
- Tennessee Valley Authority
- Tennessee Technological University
- State of California
- Oak Ridge National Laboratory
- Texas A & M University
| Test Facility | Transfer | Results % Reduction Heat |
|---|---|---|
| University of Mississippi |
On Top of the R-19 Insul. |
45% |
| Tennessee Valley Authority |
A. Radiant barrier in Roof Truss w/R-19 Insul. |
34% 44% |
| Oak
Ridge Federal Lab |
A. Radiant barrier in Roof Truss w/R-19 Insul. |
28% 39% |
| Florida
Solar Center Texas A & M University |
Above R-19 Insulation |
45% 46% 78.2% |
Winter TestTemperature as mild as 65% |
||
|---|---|---|
|
Northeastern Illinois University |
A. On Top
of R-19 Insulation B. Two sided Barrier, two layers separated by a 1 1/2 inch airspace |
30-50% |